As is well known, a phased array is a group of simple radiating antennas, hereinafter referred to as elements, arranged over an area called an aperture. A beam or beams is formed by superposition of the radiation emanating from all of the elements and the direction of the beam can be adjusted by varying the relative phase of the signal applied to each element or by varying the frequency of an oscillator. Because the signals at each element must be related in phase, they have heretofore been derived from a reference oscillator. The signal from the oscillator is fed to the elements of the array through various combinations of amplifiers and phase shifters, of which there are many different configurations.
The primary limitation in present phased array systems is the complexity and cost of the feed structure. Maintaining the correct phase of each element is especially difficult since phase tracking must be maintained from the reference oscillator through a combining network and phase shifters. The phase shifters are not easily made, particularly if fine adjustments over 360.degree. are required. In addition, the bandwidths of the phase shifters are relatively narrow. The use of digital phase shifters implies a quantization of the phase. If the quantization is coarse, the side lobe levels of the beam are increased and it is generally not presently feasible to produce phased array systems with very low side lobe levels because of the cost and complexity of making digital phase shifters which provide fine phase control.